General approach to rashes
Contents
Background
Dermatology Nomenclature
Small lesions (<0.5cm)
| Name | Raised/Palpable | Fluid-Filled | Other Description | Diagram |
| Macule | No | None | flat, cirumscribed, colored | 
|
| Papule | Yes | None | Solid | 
|
| Vesicle | Yes | Clear | .png)
| |
| Pustule | Yes | Pus | Leukocytes or keratin | 
|
Large lesions (>0.5cm)
| Name | Raised/Palpable | Fluid-Filled | Other Description | Diagram |
| Patch | No | None | Large macule (flat, colored) | 
|
| Plaque | Yes | None | Superficially raised, circumscribed solid area | 
|
| Nodule | Yes | None | Distinct large papule | 
|
| Bulla | Yes | Clear | Large vesicle/blister or exposed epidermal layer | 
|
| Wheal | Yes | Edema | Firm and edema of dermis |
Other
Differential Diagnosis
Rash
- Acute generalized exanthematous pustulosis
- Allergic reaction
- Aphthous stomatitis
- Atopic dermatitis
- Chickenpox
- Chikungunya
- Coxsackie
- Dermatitis herpetiformis
- Erysipelas
- Exfoliative erythroderma
- Impetigo
- Measles
- Miliaria (Heat Rash)
- Necrotizing fasciitis
- Pellagra
- Poison Oak, Ivy, Sumac
- Psoriasis
- Pityriasis rosea
- Scabies
- Seborrheic dermatitis
- Serum Sickness
- Smallpox
- Shingles
- Tinea capitus
- Tinea corporis
- Vitiligo
Rash visual diagnosis
Poison ivy/Oak/Sumac
Poison ivy/Oak/Sumac
Psoriasis before and after treatment.
Hyperpigmentation
- Postinflammatory hyperpigmentation (acne, Psoriasis, atopic and contact dermatitis, lichen planus, trauma, drugs, and fixed-drug eruptions)
- Melasma
- Solar lentigines
- Ephelides (freckles)
- Café-au-lait macules
- Nevi
- Melanoma and precursors
Hypopigmentation
- Vitiligo
- Pityriasis alba
- Tinea versicolor
- Postinflammatory hypopigmentation
- Piebaldism
- Tuberous sclerosis
- Hypomelanosis of Ito